RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 127 



misnomer to call this a " humus determination." On the other hand r 

 the amount of humified material is important as a possible source of 

 nitrogen, it being, according to Hilgard (125), " wholly uncertain to 

 what extent the unhumified material will ultimately become humus, 

 from the nitrification of which plants are presumed to chiefly derive 

 their nitrogen." 



Loss on ignition. 



Loss on ignition, as has been said, may be of interest in connection 

 with water-holding properties. It is readily determined by placing 

 approximately 100 grams of the soil in a shallow earthen or platinum 

 dish, in which it will first be oven-dried and weighed and then heated 

 to red heat in a gasoline or electric oven, with a moderate current of 

 air pressing over it. Providing lumps have been broken down at the 

 outset, the oxidation may usually be completed in an hour. After 

 this the sample is again weighed, the ignition loss is calculated, and 

 the percentage of loss is based on the oven-dry weight of the sample- 



In the case of soils containing considerable lime or magnesium car- 

 bonate, the error through the breaking down of these on ignition may 

 be largely eliminated by a preliminary treatment with dilute hydro- 

 chloric acid, as in the humus extraction method. 



The ammonia-soluble humus. 



The ammonia-soluble humus, or matiere noire of Grandeau (122) 

 is the aim of all of the more recent methods of extraction. Lime and 

 magnesia are first removed by washing the soil with dilute hydro- 

 chloric acid. Grandeau mixed the washed soil with coarse sand 

 and placed it in a funnel at the bottom of which were fragments of 

 glass or porcelain. The whole mass was then moistened with dilute 

 ammonia and allowed to digest for three or four hours, after which 

 the solution was washed through with water or water containing a 

 little ammonia. The filtrate was then evaporated to dryness, weighed,, 

 ignited in a platinum dish, and weighed again. The loss on ignition 

 is the measure of the extractable humus. The residue is termed 

 humus ash. 



Hilgard 19 modified the Grandeau method by placing the soil in a 

 paper filter, covering it with a disk of filter paper, and here perform- 

 ing both the acid washing and the ammoniacal extraction. The latter 

 is accomplished with 4 per cent ammonia water until the filtrate comes 

 through colorless. 



Others have attempted to improve on Hilgard's method in order 

 to expedite the process; but, as shown by Alway, Files, and Pinckney 

 (101), they have introduced serious error through including in the 

 ammoniacal extract considerable amounts of colloidal clav which, on 



19 In Bulletin 3X, Bureau of Chemistry, United States Department of Agriculture, 1893. 



